AX5 4200, cannot get internet after installing the app & wifi

What router do you have? AX4200 is a speed, not a model

What modem/gateway is it connected to? 

If this is a new device, support is free for the first 90 days from purchase. 

To get a hold of support. Click on "MyNetgear" at the top.
Register an account (or login) and then the device.
From there you can start the support process. Keep in mind that its only free for the first 90 days.